The present application finds particular application in hybrid commercial vehicle brake systems, particularly involving air demand in a vehicle air system. However, it will be appreciated that the described technique may also find application in other air systems, other vehicle systems, or other motor control systems.
In heavy duty hybrid vehicle design, there is often an effort to electrify vehicle subsystems so as to move them off the engine. As these subsystems are electrified, there is a need for these subsystems to intelligently control and optimize their power usage to be in concert with the entire vehicle electrical system. Specifically, there is a problem with existing electric air compressor subsystems within heavy duty hybrid vehicles. Presently, electric air compressor systems are not designed to manage and modify their operation so as to control and optimize the energy used to charge the air tanks for air brake and other pneumatic systems. That is, while electric compressor systems exist on heavy duty hybrid vehicles, there is a problem with these systems in that they do not include an intelligent control of the energy required to maintain the air pressure. These systems do not monitor or utilize existing vehicle information to modify their operation to optimize energy conservation. Existing compressor systems normally turn the compressor on or off at fixed speeds and pressures: the compressor is on at full speed at the lower pressure (cut-in) pressure and off at the higher (cut-out) pressure. Existing electric compressor systems do not dynamically alter their operation to conserve or store energy. Conventional electric compressor systems have no way to optimize energy usage desired to maintain vehicle air pressure or modify the compressor operation based upon vehicle status or energy demands.
Classical compressor control systems do not have the capability to dynamically vary motor speed (RPM) or change the cut-in and/or cut-out pressure thresholds as vehicle operational status and power requirements change. Extant air compressor control systems do not modify their operation during periods of high air demand. High air demand may be caused by high brake demand and/or auxiliary system air demand. High brake demand often occurs in heavy city traffic or on roads undergoing construction. High air demand for auxiliary systems often occurs in city buses with “kneeling” or load-leveling functions to facilitate passenger entry/exit. During periods of high air demand, existing systems turn a compressor motor on or off at fixed cut-in and cut-out pressure thresholds and drive the compressor motor at its fixed maximum RPM. Such conventional systems do not modify their operation to optimize air supply efficiency.
One classical approach relates to an engine driven compressor wherein the engine speed is modified according to the operating needs of the compressor, with discrete engine speeds corresponding to changing air demand. The controller can disengage the compressor from the engine if the air demand is low and other loads need the engine power. Another approach relates to an electronic compressor control system that measures air demand conditions at the reservoir. Under high demand, a pressure unloader valve is used to control the compressor. Under low demand, the controller shuts off the compressor motor entirely.
Another conventional approach relates to an electronically controlled air compressor that absorbs engine energy when the vehicle is coasting by filling the reservoirs to a higher than normal pressure. The compressor is shut off to reduce the load on the engine in certain circumstances, unless the pressure is lower than mandated. Yet another approach relates to a compressor controller that changes the electric drive motor rpm to keep the reservoirs at a set pressure. Other techniques relate to a portable compressed air system. In order to meet an increased air demand, the compressor motor speed is increased. If additional systems need the motor, the compressor can be detached entirely.
Other approaches relate to a system with a main compressor for air brake units powered by the engine and an auxiliary electrically driven compressor for high pressure systems. A central controller determines which compressor should be operational, or both, based on the air demand. In some cases, a compressor control system can vary a target pressure based on vehicle running states, such as anticipated demand of the suspension system, which requires a higher operating pressure than 10 bar. When the vehicle is coasting, the target pressure in the reservoirs is set to be higher to take advantage of free energy of the engine. The target reservoir pressure during the engine off mode is always higher than the engine on mode. Still other techniques relate to an electronically controlled air conditioning compressor. The compressor is driven such that the rotation speed of the compressor is increased when the vehicle speed is decreased. In this manner, the electrical load created by the compressor is reduced and absorbed by the engine.
The present innovation provides new and improved systems and methods for controlling compressor motor operation mode as a function of vehicle air demand in a vehicle air system, which overcome the above-referenced problems and others.